Lubricating oil thickened to a grease consistency with a metal salt of orotic acid



United States Patent 3,149, 76 LUBRKCATENG GEL THZCKENED T0 A GREASE CQN ETENCY WITH A METAL SALT @F GROTEC ACED Eohu F. Hedenburg, ChesWi-cir, and loseph X. Iii'cGrath,

Monroeviile, Pa., assignors to Quit Research dz Development Company, Pittsburgh, Pa, a corporation 0r Deiaware No Drawing. Fiiesl Mar. 8, 1062, Ser. N 178,284 Claims. (Cl. 252-33.6)

This invention relates to improved lubricating compositions and more particularly to lubricants suitable for high temperature lubrication.

The trend in design of modern aircraft has accentuated the need for greases which will lubricate anti-friction bearings operating at high rotational speeds and high temperatures. While considerable progress has been made in recent years in producing improved aircraft greases some dificulty has been encountered in producing a grease which will eifectively lubricate bearings operating at high rotational speeds and high temperatures for prolonged periods of time. Conventional aircraft greases currently available have failed to meet the stringent requirements on such a lubricant. I

We have discovered that a lubricating composition having improved lubricating charcteristics for an extended period of time when used to lubricate bearings operating at an elevated temperature under high rotational speeds can be obtained by incorporating into a lubricating oil in oil thickening proportions an alkali metal salt of orotic acid. Thus, the improved lubricating composition of our invention comprises a dispersion in a lubricating oil of a sufiicient amount to thicken the lubricating oil to a grease consistency of an alkali metal salt of orotic acid.

The alkali metal salt of orotic acid can be prepared by treating orotic acid with an aqueous alkali solution. Neither the compounds per se nor their method of preparation constitutes any portion of the invention. For example, sodium orotate can be prepared by reacting aqueous sodium hydroxide and orotic acid in equimolar proportions at 80 C. The amount or" the alkali metal salt of orotic acid which we use is an amount sufiicient to thicken the lubricating oil to a grease consistency. In general, this amount comprises about to about 50 percent by weight of the total composition.

The lubricating oil in which the alkali metal salt of orotic acid is incorporated is preferably a lubricant of the type best suited for the particular use for which the ultimate composition is designed. Since many of the properties possessed by the lubricating oil are imparted to the ultimate lubricating composition, we advantageously employ an oil which is thermally stable at the contemplated lubricating temperature. Some mineral oils, especially hydrotreated mineral oils, are sufiiciently stable to provide a lubricating base for preparing lubricants to be used under moderately elevated temperatures. Where temperatures in the order of 400 F. and above are to be encountered, synthetic oils form a preferred class of lubricating bases because of their high thermal stability. The synthetic oil can be an organic ester which has a majority of the properties of a hydrocarbon oil of lubricating grade such as di-Z-ethylhexyl sebacate, dioctyl phthalate and dioctyl azelate. Instead of an organic ester, we can use polymerized olefins, copolymers of alkylene glycols and alkylene oxides, polyorgano siloxanes, polyaryl ethers and the like.

The liquid polyorgano siloxanes and certain polyaryl ethers because of their exceedingly high thermal stability form a preferred group of synthetic oils to which the alkali metal salt of orotic acid is added. The polyorgano siloxanes are known commercially as silicones and are made up of silicon and oxygen atoms wherein the silicon atoms may be substituted with alkyl, aryl, alkaryl, aralkyl and cycloalkyl radicals. Exemplary of such compounds are the dimethyl silicone polymers, diethyl silicone polymers, ethyl-phenyl silicone polymers and methyl-phenyl silicone polymers. Exemplary of an exceedingly good polyaryl ether is a poly-phenyl ether, i.e., m-bis(m-phenoxyphenoxy) benzene.

If desired, a blend of oils of suitable viscosity may be employed as the lubricating oil base instead of a single oil by means of which any desired viscosity may be secured. Therefore, depending upon the particular use for which the ultimate composition is designed, the lubricating oil base may be a mineral oil, a synthetic oil, or a mix ture of mineral and/ or synthetic oils. The lubricating oil content of the compositions prepared according to this invention comprises about 50 to about percent by weight of the total composition.

In compounding the compositions of the present invention, various mixing and blending procedures may be used. In a preferred embodimet of the invention, the lubricating oil and the alkali metal salt of orotic acid together with conventional lubricant additives, if desired, are mixed together at room temperature for a period of 10 to 30 minutes to form a slurry. During this initial mixing period some thickening is evidenced. Some lumps may be formed. The slurry thus formed is then subjected to a conventional milling operation in a ball mill, a colloid mill, homogenizer or similar device used in compounding greases to give the desired degree of dispersion. In the illustrative composition of this invention, the slurry was passed twice, by means of a pump, through a Premier Colloid Mill set at a stator-rotor clearance of 0.002 inch. Maximum thickening occurred on the second pass through the mill.

The lubricating composition of this invention can contain conventional lubricant additives, if desired, to improve other specific properties of the lubricant without departing from the scope of the invention. Thus, the lubricating composition can contain a filler, a corrosion and rust. inhibitor, an extreme pressure agent, an antioxidant, a metal deactivator, a dye and the like. Whether or not such additives are employed and the amounts thereof depend to a large extent upon the severity of the conditions to which the composition is subjected and upon the stability of the lubricating oil base in the first instance. Since the polyorganosiloxanes, for example, are in general more stable than mineral oils, they require the addition of very little, if any, oxidation inhibitor. When such conventional additives are used they are generally added in amounts between about 0.01 and 5 percent by weight based on the weight of the total composition.

In order to illustrate the lubricating characteristics of grease compositions of the invention at 20,000 revolutions per minute and at a temperature of 400 F., Pope spindles were used in a test procedure similar to that outlined by the Coordinating Research Council Tentative Draft (July 1954), Research Technique for the Deter 204 ball hearing. In general, bearings fabricated from high speed tool steel and ball retainers fabricated from silver-plated beryllium-copper (MRC 204-847) are used as both test and outboard bearings. The bearing assembly which is mounted on a horizontal spindle is subjected to a radial load of 5 pounds. The portion of the spindle upon which the test bearing assembly is located is encased in a thermostatically controlled oven. By this means the temperature of the bearing can be maintained at a desired elevated temperature which in the test reported hereinafter was 400 F. The spindle is driven by a constant belt-tension motor drive assembly, capable of giving spindle speeds of 20,000 revolutions per minute. The spindle is operated on a cycling schedule consisting of a series of periods, each period consisting of hours running time and 4 hours shutdown time. The test continues until the lubricant fails. The lubricant is considered to have failed when any one of the following conditions occurs, (1) spindle input power increases to a value approximately 300 percent above the steady state condition at the test temperature; (2) an increase in temperature at the test bearing of 20 F. over the test temperature during any portion of a cycle; or (3) the test bearing locks or the drive belt slips at the start or during the test cycle.

The lubricating oil used in preparing the lubricating composition summarized in Table I Was a synthetic oil known commercially as DC 550 Fluid marketed by Dow- Corning Corporation. DC 550 Fluid is a methylphenylsiloxane polymer having as typical characteristics a viscosity at 100 F. of 300 to 400 SUS, a viscosity-tempera ture coecient of 0.75, a freezing point of 50 F., a flash point of 600 F. and a specific gravity C./25 C. of 1.08.

In preparing the lubricating composition, the oil and the alkali metal salt of orotic acid were mixed at room temperature for a period of 10 to minutes. The slurry thus formed Was passed twice through a Premier Colloid Mill set at a stator-rotor clearance of 0.002 inch. The thickened lubricating composition thus prepared had the following approximate make-up and properties.

Table I Composition, percent by Weight: A Lubricating oil, DC 550 Fluid 74 Sodium orotate 26 Inspection:

Penetration (ASTM D21752T)- Unworked 237 Worked 237 Dropping point, F. (ASTM D566-42) 900+ Performance life, hrs., 20,000 rpm. at

The long performance life of the composition of the invention at a high rotational speed and a high temperature is self evident from the above data. Composition A contrary to most thickened lubricants becomes more viscous upon heating. This is a desirable property in that it will reduce undesirable loss of the fluid during use at elevated temperatures.

Other lubricating compositions within the scope of the invention are illustrated in Table II. GE, Silicone 81717 It has a viscosity at F. of 3487 centistokes, at 0 F. of'390 centistokes, at 100 F. of 71.3 centistokes, at 210 F. of 22 centistokes and at 700 F. of 1.9 centistokes. QF-6-7024 Fluid and QF-67039 Fluid are marketed by Dow-Corning Corporation. QF-6-7024 Fluid is considered to be a methylphenylsiloxane polymer wherein the end silicon atoms are substituted to a high degree by two phenyl groups and one methyl group. The material is highly resistant to radiation. QF-67039 Fluid is believed to be a methylphenylsiloxane polymer inhibited against deterioration and otherwise similar to QF-6-7024 Fluid.

Table II Composition, Percent By Weight B G While our invention has been described with reference to various specific examples and embodiments, it will be understood that the invention is not limited to such examples and embodiments and may be variously practiced within the scope of the claims hereinafter made.

We claim:

1. A lubricating composition comprising a dispersion in a lubricating oil selected from the group consisting of polyorgano siloxanes, organic esters and polyaryl ethers of a suificient amount to thicken the lubricating oil to a grease consistency of an alkali metal salt of orotic acid.

2. The composition of claim 1 wherein the lubricating oil is a polyorgano siloxane.

3. A lubricating composition comprising a dispersion in a liquid polyorgano siloxane of a sufficient amount to thicken the polyorgano siloxane to a grease consistency of sodium orotate.

4. A lubricating composition comprising a dispersion in a liquid polyorgano siloxane of a sufiicient amount to thicken the polyorgano siloxane to a grease consistency of potassium orotate.

5. A lubricating composition comprising a dispersion in a liquid polyorgano siloxane of a sufficient amount to thicken the polyorgano siloxane to a grease consistency of lithium orotate.

References Cited in the file of this patent UNITED STATES PATENTS 2,372,588 Larsen et al. Mar. 27, 1945 

1. A LUBRICATING COMPOSITION COMPRISING A DISPERSION IN A LUBRICATING OIL SELECTED FROM THE GROUP CONSISTING OF POLYORGANO SILOXANES, ORGANIC ESTERS AND POLYARYL ETHERS OF A SUFFICIENT AMOUNT TO THICKEN THE LUBRICATING OIL TO A GREASE CONSISTENCY OF AN ALKYLI METAL SALT OF OROTIC ACID. 